Field of the Invention
The invention relates to a method and apparatus for reversing sheet material in sheet-processing machines, such as sheet-fed printing presses, having a plurality of printing units disposed one behind another.
German Patent DE 26 33 183 C, corresponding to U.S. Pat. No. 4,165,689 to Giuiuzza, relates to an apparatus for reversing sheets in a multicolor rotary offset printing press. Such a press includes at least two printing units each having a plate cylinder, a transfer cylinder, and an impression cylinder, which are coupled together in terms of drive through circulating transmission elements. A reversing device associated with the transfer elements is provided, which includes a reversing cylinder having a gripper.
The gripper is driven and disposed such that the sheets that have already been printed on one side are gripped after they have passed a transfer cylinder and the sheets have been removed completely from a transfer device resting on the cylinder. The sheets printed on one side are gripped by a reversal mechanism, which acts at the trailing edge of the sheets, which, until this point, have still been held at the leading edge by the gripper of the reversing cylinder. As a result, these sheets are fed to the gripper of the transfer device again with the direction of advance reversed by a separate apparatus that can be configured as a swing gripper or as a table to which vacuum is applied.
German Published, Non-Prosecuted Patent Application DE 39 03 093 A1 discloses a sheet-reversing apparatus. According to such a solution of a sheet-reversing apparatus for in-line rotary printing presses, the impression cylinders of successive printing units are connected by at least one transfer drum. A storage drum is disposed downstream of a transfer drum, parallel to the recto printing sheet guidance. The sheet-reversing apparatus can be uncoupled from the rectoprint sheet guide cylinders during recto printing operation. Provided on a sheet-reversing apparatus is a format adjustment, which can be adjusted independently of the cylinders carrying sheets in recto printing.
German Published, Non-Prosecuted Patent Application DE 198 33 903 A1, corresponding to U.S. Pat. No. 6,401,610 to Becker et al., relates to a method for the transfer of a sheet trailing edge from an upstream cylinder of a sheet-fed rotary printing press. According to such a method for the transfer of the sheet trailing edge from a cylinder and its transfer to a gripper system of a reversing drum, a suction gripper is guided initially along the periphery of the cylinder until the suction gripper has securely gripped the sheet trailing edge. The trailing edge is then guided tangentially to the cylinder cover of the upstream cylinder into the periphery of the reversing drum, the sheet being tautened and end-compressed along a tangent to the cylinder. The sheet is then transferred under no tension to the gripper system of the reversing drum. A gear device used for such a purpose includes three drive systems that are coupled to one another and are controlled through stationary cams.
In single-drum reversing systems, in which the impression cylinder located upstream of the reversing drum acts as a storage drum in a perfecting mode (also referred to as a recto/verso mode or reversing mode), the storage length is not sufficient for a large-format sheet. Attempts have been made to peel the sheet material off the impression cylinder, according to a solution disclosed by German Published, Non-Prosecuted Patent Application DE 44 24 968, but problems have occurred with regard to in-register transfer of the sheet trailing edge. By placing pressure elements, attempts have been made to press onto the sheet, but this, in turn, entails problems with regard to smearing in the case of those sheets that do not have any print-free areas.
It is accordingly an object of the invention to provide a method and apparatus for reversing sheet material in sheet-processing machines that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that turns large-format sheet material in register when the overall space is limited.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method for reversing sheet material having edges in a sheet-processing machine having at least two printing units, including the steps of providing a gripper system on a reversing drum associated with at least one of the printing units, providing an impression cylinder operable as a storage drum in a recto/verso mode, the storage drum having a recto printing side and an impression-cylinder-side gripper system, the storage drum and the reversing drum defining a transfer centerline therebetween, and gripping, in the recto/verso mode, one of the edges of the sheet material at an angle before the transfer centerline with a holding and lifting system disposed parallel to the recto printing side of the storage drum before an edge of the sheet material fixed to the storage drum is released by the impression-cylinder-side gripper system.
With the objects of the invention in view, there is also provided a method for reversing sheet material having edges in a sheet-processing machine having at least two printing units, including the steps of providing a gripper system on a reversing drum associated with at least one of the printing units, providing an impression cylinder operable as a storage drum in a recto/verso mode, the storage drum having a recto printing side and an impression-cylinder-side gripper system, the storage drum and the reversing drum defining a transfer centerline therebetween, gripping a given edge of the sheet material with the impression-cylinder-side gripper system, and gripping, in the recto/verso mode, a given edge of the sheet material at an angle before the transfer centerline with a holding and lifting system disposed parallel to the recto printing side of the storage drum before the given edge is released by the impression-cylinder-side gripper system.
The advantages of the solution according to the invention can primarily be seen in the fact that, as a result of the early gripping of the sheet material at one edge before it passes the transfer centerline, early opening of the holding systems of the storage drum that grip the sheet material can be brought about. Such a configuration ensures that sheet material needing a large storage length can assume a substantially extended position underneath the storage drum. This prevents the sheet material from being able to run into the pocket area between storage drum and the transfer cylinder upstream of the latter and being damaged.
The holding and lifting system disposed outside the reversing drum tensions the sheet before it is turned and transfers the sheet to the gripper system of the reversing drum. The configuration ensures that the sheet material is transferred in register to the reversing drum so that both sides of the sheet material can be printed with the same quality. The in-register gripping of the sheet trailing edge of the sheet material is ensured by the fact that, at the time that it is gripped, a frictional or positive connection between the holding and lifting system and the outer surface of the impression cylinder serving as a storage drum is produced.
In a development of the idea on which the invention is based, the trailing edge of the sheet material is attracted by suction to the circumference of the storage drum before reaching the transfer centerline and is tensioned in the circumferential direction. Gripping the sheet trailing edge of the sheet material in the tensioned state of the sheet material ensures its in-register gripping and transfer to the reversing drum downstream of the storage drum. In accordance with the method proposed by the invention, the edge of the sheet material fixed to the circumference of the storage drum is released before it reaches a pocket between the storage drum and a transfer drum upstream of the latter. The early release of the edge of the sheet material fixed to the storage drum permits the deflection of large-format sheet material, needing a great storage length, into the free space underneath the storage drum so that, during the reversing action, the material does not experience any contact with rotating and stationary printing-unit components.
The assumption of a substantially extended position of the sheet material is assisted by rotation of the gripper system of the reversing drum that, during the rotation of the reversing drum, holds the gripped edge of the sheet material substantially in the horizontal position.
In accordance with another mode of the invention, a trailing edge of the sheet material is held in a gripper closure before reaching the transfer centerline.
In accordance with a further mode of the invention, one of a form-fitting connection and a frictional connection is produced between the gripper closure and the impression cylinder.
In accordance with an added mode of the invention, a transfer drum is placed upstream of the storage drum with respect to a sheet material transport direction and an edge of the sheet material fixed on a circumference of the storage drum is released before reaching a pocket between the storage drum and the transfer drum. Preferably, the pocket is disposed between the storage drum and the transfer drum at a downstream side of the storage drum with respect to a sheet material transport direction.
In accordance with an additional mode of the invention, the gripper system of the reversing drum is rotated to transfer the trailing edge of the sheet material into a substantially extended position. Preferably, the sheet material assumes the substantially extended position underneath the storage drum.
With the objects of the invention in view, there is also provided an apparatus for reversing sheet material having edges in a sheet-processing machine, including at least two printing units, at least one of the printing units having a reversing drum having a gripper system, an impression cylinder operable as a storage drum when recto/verso printing, the storage drum having a recto printing side, a circumference, and an impression-cylinder-side gripper system, the storage drum and the reversing drum defining a transfer centerline therebetween, a holding and lifting system disposed parallel to the recto printing side of the storage drum, the holding and lifting system adapted to lift an edge of the sheet material off the circumference of the storage drum before the transfer centerline and to transfer the lifted edge into the gripper system of the reversing drum one of directly and along a path.
In accordance with yet another feature of the invention, the holding and lifting system lifts one edge of the sheet material from the circumference of the storage drum before the transfer centerline and transfers the edge, directly or along a path, into the gripper system of the reversing drum.
In accordance with yet a further feature of the invention, the system is constructed as a self-supporting bridge that circulates relative to the storage drum, of which one or more can be associated with the circumference of the impression cylinder functioning as a storage drum. The holding and lifting system according to the first variant of the solution according to the invention includes a driven swinging element that can be set cyclically against the outer surface of the storage drum and that, at a distance xcfx86 before the transfer centerline between storage drum and reversing drum, has a holding element for gripping the sheet trailing edge of the sheet material accommodated on the storage drum. The holding element, in turn, includes a suction element that can be moved at right angles to the outer surface of the storage drum and with which the trailing edge of the sheet material in the circumferential direction on the storage drum can be tensioned in the radial direction and lifted off the outer surface of the storage drum. To assist the action of lifting the sheet trailing edge of the sheet material, at the moment it is gripped between the holding and lifting system and the impression cylinder functioning as a storage drum, a form-fitting or frictional connection is produced, it being possible to provide on the holding element a fixing element that can be displaced in the horizontal direction and is configured such that it can be moved into and out of the holding element. By such a displaceable fixing element in the holding and lifting system, it is possible to move under the sheet trailing edge of the sheet material lifted off the outer surface of the storage drum so that it is ensured that the sheet trailing edge of the sheet material, to be gripped in register, is gripped by the gripper system associated with the reversing drum in a tension and aligned state.
In accordance with yet an added feature of the invention, the holding element has a holding finger adapted to move under the trailing edge of the sheet and to lift off the trailing edge from the outer surface of the storage drum.
In accordance with yet an additional feature of the invention, the holding and lifting system is constructed substantially as a swinging gripper driven by an eccentric drive. The movement path of the swinging gripper relative to the storage drum or relative to the reversing drum is imposed by the eccentric drive, which executes two complete revolutions per 360xc2x0 machine angle and substantially impresses onto the swinging gripper a movement path running in the shape of a loop. By the holding and lifting system disposed above storage drum and reversing drum according to this variant, the sheet trailing edge picked up from the outer surface of the storage drum is transferred in-register to the gripper system of the reversing drum. According to this variant, the holding and lifting system is moved out of the reversing drum and is constructed as a separate transfer system on the side of the printing unit for the sheet material to be turned.
In accordance with again another feature of the invention, the holding and lifting system can be constructed as a rotating pair of cylinders, on which a plurality of sucker/gripper systems are provided. By such a configuration of the holding and lifting system, the sheet trailing edge of the sheet material accommodated on the outer surface of the storage drum can be gripped early, before passing the transfer centerline, and can be transferred along a movement path from one transfer cylinder to the further transfer cylinders before it is gripped by the gripper system of the reversing drum. According to this variant, the transfer of the trailing edge of the sheet material to be turned is not carried out directly to the gripper system of the reversing drum but indirectly through the interposition of the holding and lifting system, constructed as a rotating pair of cylinders.
In accordance with again a further feature of the invention, the pair of cylinders include first and second transfer cylinders, the first transfer cylinder is adapted to pick up the trailing edge of the sheet from the outer surface of the storage drum and to transfer the trailing edge to the second transfer cylinder along a gripper path, and the second transfer cylinder is adapted to transfer the trailing edge to the gripper system of the reversing drum along the gripper path.
In accordance with a concomitant feature of the invention, the rotating cylinders of the pair of cylinders are constructed as a transfer cylinder equipped with a plurality of gripper and sucker system and, preferably, constructed as double disks, between which the sucker/gripper systems are accommodated as self-supporting bridge parts.
The method proposed according to the invention and the solution proposed according to the invention, in accordance with the variants illustrated, can preferably be used on sheet-processing multicolor rotary printing presses. If stiffer printing materials, such as board, or those materials requiring a large storage length during reversing, are processed on web-processing rotary printing presses having two and more printing units and downstream finishing or varnishing units, the use of the method proposed according to the invention and the apparatus proposed according to the invention permits smear-free in-register reversing to be achieved because the printing material to be turned is effectively protected against contact with printing-unit components accommodated in a stationary or rotating manner.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an apparatus for reversing sheet material in sheet-processing machines, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.